The proposed experiments address several fundamental issues concerning how integral membrane proteins are altered by naturally-occurring mutations, and how the cell responds to such mutant proteins. The research may contribute to an improved understanding of the pathology of diseases die to mutant membrane proteins, such as cystic fibrosis and hereditary blindness. The experiments focus on E. coli lac permease as a simple model. The research investigates two different classes of mutations: those that inactivate lac permease and those that render the protein toxic to cells. We propose to determine whether representative inactivating mutations primarily alter the establishment of membrane topology, the folding of the membrane-inserted polypeptide, or the transport activity of lac permease. Other experiments will attempt to identify cell proteases that degrade mutant lac permeases, and examine whether the expression of mutant lac permeases induces a cellular "stress" response.